Divide a circle into several parts evenly and make it into an approximate rectangle. The length of the approximate rectangle is 12.56 decimeters. How many square decimeters is the area of the circle?

If the length of the rectangle is half of the circumference of the circle, then 2 * 3.14 * r = 2 * 12.56, so r = 4
Area s = 3.14 * 4 ^ 2 = 50.24 square decimeters

Use three 12.56 meters iron wires to form a square, a rectangle (the length of the rectangle is 4 meters) and a circle. Are they the same area?

A 12.56 decimeter long wire is enclosed into a square and a circle respectively, and the area of the circle and the square is calculated

Side length of square = 12.56 △ 4 = 3.14 (decimeter)
The area of a square
=3.14×3.14
=9.8596 (square decimeter)
Radius of a circle
=12.56÷3.14÷2
=2 (decimeter)
Area of a circle
=3.14×2×2
=12.56 (square decimeter)

Use two 12.56 cm long wires to form a square and a circle respectively. Which area is larger? How much bigger?

12.56 △ 4 = 3.14 (CM), 3.14 × 3.14 = 9.8596 (CM), 12.56 △ 3.14 △ 2 = 2 (CM), 3.14 × 22 = 12.56 (CM), 12.56-9.8596 = 2.7004 (CM); answer: the area of circle is large, 2.7004 square cm

Use two 12.56 decimeter iron wires, one to form a square and the other to form a circle. The area ratio of the square to the circle is (): ()

Square area: (12.56 ／ 4) × (12.56 ／ 4) = 9.8596 (square decimeter)
The area of the circle is: 3.14 × (12.56 △ 3.14 △ 2) ^ 2 = 12.56 (square decimeter)
The area ratio of square to circle is 9.8596:12.56 = 157:200

After cutting a round piece of paper, put it together into an approximate rectangle with the width equal to the radius and the area unchanged. The circumference of the rectangle is 12.56 cm, and the circle is 12.56 cm
What's the area of this round piece of paper?

Radius = 12.56 △ 3.14 △ 2 = 2cm;
Length = 12.56 △ 2 = 6.28cm;
Area = 2 × 6.28 = 12.56 square centimeter
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After cutting a circular piece of paper, put it together into an approximate rectangle with the width equal to the radius and the area unchanged. The perimeter of the rectangle is 16.56 cm. What is the area of the cut circular piece of paper in square cm?

Let the radius of this circle be r. according to the meaning of the question, we can get: 2 × 3.14r + 2R = 16.56, & nbsp; & nbsp; 6.28r + 2R = 16.56, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 8.28r = 16.56, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; r = 2, 3.14 × 22, = 3.14 ×

After cutting a circular piece of paper, put it together into an approximate rectangle with the width equal to the radius and the area unchanged. The perimeter of the rectangle is 16.56 cm. What is the area of the cut circular piece of paper in square cm?

A circle is evenly divided into several identical small sectors and cut into approximate rectangles. The circumference of the rectangle is 10cm longer than that of the original rectangle
A circle is divided into several identical small sectors and cut into an approximate rectangle. The perimeter of the rectangle is 10 cm longer than the original. The surface area of the rectangle is ()

Divide a circle into several identical small sectors and cut them into an approximate rectangle. The perimeter of the rectangle is 10cm longer than the original perimeter. The surface area of the rectangle is (78.5 square centimeter)
The extra perimeter of 10 cm is two radii, and the radius of one is 10 △ 2 = 5 cm
Area: rectangle area = original circle area
5 × 5 × 3.14 = 78.5 square centimeter

The sum of the circumference, diameter and radius of a circle is 18.56 cm. The radius of the circle is Cm, the area is Square centimeter

Let the radius of the circle be r, then the diameter is 2R and the circumference is 2 π R. from the meaning of the question, we can get: & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; if the radius of the circle is r, then the diameter is 2R and the circumference is 2 π R; If r = 2, the area of the circle is 3.14 × 22 = 12.56 (CM); answer: the radius of the circle is 2 cm, and the area is 12.56 square cm

Divide a circle into several parts evenly and make it into an approximate rectangle. The length of the approximate rectangle is 12.56 decimeters. How many square decimeters is the area of the circle?